Manipulation of competing ferromagnetic and antiferromagnetic domains in exchange-biased nanostructures

Abstract

Using photoemission electron microscopy combined with x-ray magnetic circular dichroism we show that a progressive spatial confinement of a ferromagnet (FM), either through thickness variation or laterally via patterning, actively controls the domains of uncompensated spins in the antiferromagnet (AF) in exchange-biased systems. Direct observations of the spin structure in both sides of the FM/AF interface in a model system, $\mathrm{Ni}/\mathrm{Fe}{\mathrm{F}}_{2}$, show that the spin structure is determined by the balance between the competing FM and AF magnetic energies. Coexistence of exchange bias domains, with opposite directions, can be established in $\mathrm{Ni}/\mathrm{Fe}{\mathrm{F}}_{2}$ bilayers for Ni thicknesses below 10 nm. Patterning the $\mathrm{Ni}/\mathrm{Fe}{\mathrm{F}}_{2}$ heterostructures with antidots destabilizes the FM state, enhancing the formation of opposite exchange bias domains below a critical antidot separation of the order of a few $\mathrm{Fe}{\mathrm{F}}_{2}$ crystal domains. The results suggest that dimensional confinement of the FM may be used to manipulate the AF spin structure in spintronic devices and ultrahigh-density information storage media. The underlying mechanism of the uncompensated AF domain formation in $\mathrm{Ni}/\mathrm{Fe}{\mathrm{F}}_{2}$ may be generic to other magnetic systems with complex noncollinear FM/AF spin structures.